Billing page: no-billing state follow-ups

Found while visually checking Task 7174 (Billing page, operator plane / org with no billing, 390px and 1280px). - On Payments/Methods/Details with no billing (the route's 404) the panel under the info note is blank; render the same "Billing isn't set up yet" empty state the not-connected case uses, inside the panel, instead of a page-level note. - The info note sits above the tab strip only on the Stripe tabs, so the strip jumps ~40px down when switching from Products/Budgets to Methods; keep the strip fixed (note inside the panel fixes both). - On the operator plane ("All orgs") Billing shows an org's billing page with nothing to bill; hide Billing from the operator's nav or say which org it applies to. - The Budgets empty state's "Add budget sets one for a project or group." line (`components/billing/BudgetsList.tsx`) shows to a finance:view reader too, who has no Add budget button (`AddBudget.tsx` renders only for an org admin seat); show it only to an org admin. Out of scope: Stripe billing behaviour; budget rules and APIs. Done means: - With no billing, each Stripe tab's panel shows one empty state naming who sets billing up; no blank panel. - Switching tabs never moves the tab strip. - A finance:view reader's empty Budgets list names no button they lack.

Billing: no-billing note now inside each Stripe tab's panel, tab strip fixed, operator visit points at Customers, Budgets "Add budget" copy for admins only. Quick gate + 55 tests green, visual check done (390/1280). PR #5856 merged 17b8188. Follow-up draft #7206.